[cfe-dev] disabling loop idiom recognizer in clang

[Damjan Marion]

On Apr 30, 2011, at 7:15 PM, Eli Friedman wrote:

>> 
>> Here it is:
>> 
>> # clang -ccc-host-triple arm-unknown-freebsd  -O2 -ffreestanding -g -c i.c -o i.o
>> 
>> void func1(unsigned *b)
>> {
>>  unsigned c[17];
>>  unsigned i;
>>  for (i=0; i < 17; i++)  c[i] = 0;
>>  do { c[*b]++; b++; } while (--i);
>> }
>> 
>> will produce memset call even with -ffreestanding.
> 
> Ah... that isn't -loop-idiom triggering; that's the loop getting
> unrolled and the stores getting merged into a memset by -memcpyopt.

Is this expected behavior? If yes how it can be disabled?